As you might imagine, the status (or validity) of a backup can only be verified when and after a restore is performed. We do have several backup(s) of the old forums etc. but we did not attempt to restore them anywhere since we couldn't find a easy way to do so. (I guess I could try to even do it locally on my PC) For example, this phpbb board does not allow us to import our phpbb backups. We would need to setup our own web server and phpbb and databases and then perform the restores...
This said, the php mysql backups should be somewhat readable even without being imported in phpbb, they could be read with other tools. However I expect them to be quite large files.